The invention relates to magnetic locks.
The invention relates more particularly to magnetic locks operated by magnetic cards in which provision is made to prevent the lock being opened by sharp impacts or so-called "rapping".
Early card-operated locks were designed for installation inside a wail or door and the key was inserted into a slot in a flush-mounted faceplate. Applying impacts to the slot or to the surface of the door or wall seldom caused unlocking as the pins moved perpendicularly to the plane of the card slot, but when the same lock was housed in a box and mounted on the surface of the wall or door, or on a post for access by car drivers entering a parking garage, the top surface above the lock was available for impacting and sharp blows could often jar the pins up and down. If a non-magnetic card-shaped object was inserted in the slot during the "rapping", the lock could sometimes be unlocked. Magnetic pin card-operated locks which are susceptible to this type of tampering are described for example in U.S. Pat. Nos. 2,566,017, 2,648,729, 2,732,703, 2,769,873, 2,931,953, 3,271,983, RE27,753, 3,595,042, 3,581,030, and 3,995,145. U.S. Pat. No. 3,705,277 describes the problem and discloses a solution which utilizes a "tamper-resistant non-magnetic pin" which, when moved by a rapping impact causes the lock to remain locked by blocking movement of the slider that contains the tumbler pins.
Nearly all of the above locks were required to be mounted horizontally, (parallel to the floor), as the pins were held in locking positions mainly by gravity. However, where a steel shield plate is used to attract all the magnetic pins towards the slot, as described in U.S. Pat. No. 3,834,197, the lock is able to be mounted vertically. U.S. Pat. No. 3,995,460 describes how a magnetic pin can be used to block slider movement if the lock is rapped on the front surface in direct line with the locking pins. This "anti-rap" pin has been shown in subsequent U.S. Pat. Nos. 4,133,194, 4,676,083, 4,312,198 and 4,932,228.
Padlocks incorporating a magnetic card-operated lock such as described in U.S. Pat. No. 3,834,197 are known in the art, however this type of lock has not been successfully produced due to its possible susceptibility to being unlocked without a correct card being inserted, by rapping on the body of the lock while a blank card is in the slot, and held under constant or intermittent pressure.